Treatment of solid fuel to reduce dustiness



Patented July 22, 1941 UNITED STATE TREATMENT or SOLID FUEL To REDUCE DUSTINESS Lincoln T. Work, Yonkers, and Rudolph E. Zetterstrand, New York, N. Y., assignors to Carter Coal Company, a corporation of Delaware No Drawing. Application July 30, 1940, Serial No. 348,432

1 20 Claims.

dust, or to provide a sticky coating for the larger pieces to cause the fine particles to adhere thereto. In some instances the nature of the treatment may be to produce a strong and abrasionresistant coating for the larger piecesvwithin which fine particles are retained. The dustproofing agent may further protect the fuel against freezing under normal winter conditions by lowering the freezing point of water in contact with the surface of the fuel and thereby preventing such water from freezing and binding adjacent pieces of the fuel together to create large, solid masses which are hard to handle, as in emptying coalcars or conveying the coal fromopen and exposed piles. Any of the dust-proofing agent that is washed away from the surface of the fuel or penetrates the interior of the fuel, is ineffective and is lost.

There have been various prior efforts to produce a satisfactory composition for such dustprooflng. One type of composition heretofore employed consists wholly or in part of petroleum oils, either as distillates or residues. Such compositions are employed in an oily form or as aqueous emulsions. Those in an oily form are conventionally applied to the fuel by being sprayed thereon at a high temperature, and this constitutes a well-recognized fire hazard. Moreover, the use of fuel oil or petroleum residues in either form presents several other difllculties. The oil appears to be slowly absorbed into the interior of the fuel, while the part remaining on the surface of the fuel is oxidizable 'to a brittle form, so that within a relatively short time the efl'ectiveness of the coating in reducing dustiness is greatly impaired. Then, too, fuel oil or petroleum residues in either form have a tendency to stain and create a messy condition in bins, hoppers, delivery trucks and railroad cars. They furthermore cause an unpleasant odor to permeate thefuel and the generalvicinity of the storage space. To obviate the difficulties of odor, color and penetration of these petroleum products it has been proposed to use paraflin wax instead of fuel oil or residues, but the wax forms a coating which has less adherence and anti-dusting qualities than the other petroleum compositions.

A number of other materials have been proposed as dust-proofing agents for fuel, such as molasses, molasses-alcohol residue, glycerin foots, sulphite liquor and the like. These materials either form coatings on the fuel which are lost through abrasion, or coatings which are readily soluble in water and easily washed off, thus reducing their effectiveness in either case. Some of them do not adequately wet the fuel, and some introduce objectionable impurities, such as the sulphur in sulphite liquor.

Another material commonly used is calcium chloride, an aqueous solution of which may be sprayed on the fuel to create a hygroscopic coating. This hygroscopic coating serves to keep the fuel in a moist condition and in this way retards the dust, and further serves to lower the freezing point pf water between the pieces of fuel, so that fuel so treated is not readily frozen into masses. However, below a humidity of about 40%, calcium chloride crystallizes and is no ducing the effectiveness of the treatment. That which remains on the surface is also easily washed from the fuel by rain, being diluted and dripping away. Another objection to-the use of calcium chloride treatment is that the drippage causes corrosion of iron and steel parts of cars, conveyers, and the like.

Compositions consisting of calcium chloride solutions with the addition of starch have also been employed in an effort to increase the adherence of the coating and to reduce the corrosion caused by the calcium chloride. Treatment with such compositions is unsatisfactory with respect to both dust-proofing and corrosion and fails to meet present-day requirements. Standardized laboratory and field tests have shown that such coatings are readily washed off notwithstanding the presence of the starch, and that the treatment soon losesits effectiveness.

The object of this invention is to overcome or 'at least minimize the objections above noted,

and to that end to provide an improved treatment for dust-proofing solid carbonaceous fuel such as coal or coke by coating the external surfaces of the same with an improved dust-proofing agent consisting of an aqueous dispersion of bentonite or any material having the characteristics of bencoal and therefore readily spread upon its suror like material retains any-other ingredients that may be used and retards penetration of these ingredients into the coal. When applied to the .coal our bentonite dispersion forms a sticky film or coating to which the dust will effectively adhere, but when exposed to the atmosphere it loses some moisture and changes to a tough and slippery illm coating which is abrasion-resistant under ordinary conditions of handling of the fuel. In neither condition does it interfere with the free-flowing character of the fuel, nor is it easily washed away. It does not create a fire hazard at any time and yet does not introduce such quantities of mineral ingredients as to noticeably alter the ash content of the fuel or to produce a heavy surface coating to interfere with combustion.

It has not heretofore been known that 9. ben-' tonite dispersion is tenaciously adherent to the surface of coal; that it wets the surface of the coal and spreads upon it witha more favorable contact angle than does water alone,'and that it is not readily washed away by extraneous water,

as rain. y

Bentonite, the essential ingredient of our dustprooflng agent, is a hydrous colloidal compound of silica capable of absorbing large amounts of water and retaining at least a portion of its total water content under normal atmospheric humidityconditions and particularly under the conditions existing in the normal handling and storage of fuel. Specifically, it is a hydrous aluminum silicate capable of swelling in water to many times its dry volume. This material may be distinguished from common clay by its extreme stickiness when wet, and its great viscosity and capacity of swelling to form a gel when dispersed in water. It may be further distinguished from clay by the fact that, on ignition at ,red heat, ordinary air-dried clay may yield around 12 to 15% loss, chiefly water, while ordinary air-dried bentonite may yield 40% to loss in weight which is also mainly water. Thus it may be seen that the ignited mass of an ordinary dry clay represents about 85% of the orisi-- nal dry weight, whereas the ignited mass of bentonite is about half its original dry weight. It is believed that bentonite possesses certain of these large differences over common clay through-the fact that it has strong secondary valence forces which cause the large amounts of water to remain attached to it while common clay does not.

Bentonite in water to the extent of, for instance,

0.5 pound in 1 gallon swells to an apparently homogeneous mass with the water and does not settle therefrom on standing, whereas clay in water in the same proportions forms a nonhomogeneous suspension fromwhich practically all of the solid matter will settle on standing for 24 hours. Furthermore, a suspension of common clay dries to a discontinuous, non-adherent form which is easily removed by being either rubbed or washed away, while a bentonite dispersion yields a continuous adherent flhn when it loses part of its water on exposure to the atmosphere. It is therefore possible to employ a bentonite dispersion as a dust-proofing agent whereas a clay suspension is not satisfactory.

The properties which have been described for bentonite may be found but usually to a lesser degree, in certain other hydrous colloidal comterials maybe employed in leu of bentonite in ,providing a dust-proofing agent according to the present invention.

In order to enhance the maintenance-of the bentonite in a moist condition which we flnd has the greater emciency in dust-proofing, a suitable hygroscopic agent may be added to the hentonite dispersions. For this purpose a single material may be employed or a combination of. materials, provided the single material or the resultant of the combination of materials is such a suitable hygroscopic agent. While the term hygroscopic is sometimes used in a very broad sense, the term hygroscopic agent is here used to comprise those materials or combinations thereof, whether liquid or solid, which in normal atmospheres attract and retain moisture to remain fluid or as a tacky mass and which do not prevent, injure or destroy the bentonite dispersion. The term therefore covers more than de-- dispersion becomes stiffer or more viscous. The

hygroscopic sugar materials possess a certain tackiness which improves the sticky character of the bentonite dispersion and thus further aids the coating in performing its dust-proofing function. It is desirable when large amounts of deliquescent earth chlorides are employed in our dustprooflng agent, to add a small amount of a heavy metal soap, that is to say, a saponiflcation product such as aluminum, zinc, calcium or lead, with. various resins, or with stearic, oleic or palmitic acids. In such case, the soap promotes the stability of the dispersion by tending to ofiset the salt effect and the base exchange on the bentonite. Since soaps of this class are water insoluble and water repellent, we find it advantageous to use a wetting agent to disperse the soap, preferably one of the sodium alcohol sulphate series, such as one now known as tergitolt (Tergitols" are sodium secondary-alcohols containing ten to twenty-one carbon atoms near the. center of the hydrocarbon chain.) We do not, however, limit ourselves to this particular type of wetting agent, since other wetting agents would also serve the purpose.

The bentonite which we have used and which we believe to be preferable, was an air-floated 200 mesh Wyoming bentonite. With it we have made and tested for anti-dusting effectiveness a number of bentonite-water dispersions as well as bentonite-water dispersions containing hygroscopic agents with or without the addition of heavy metal soap and a wetting agent therefor.

Results were satisfactory for the bentonite-wa- ,ter' dispersion, with or without other ingredients,

when from 0.2 to 0.6 pound of bentonite was used per gallon of the treating composition.

' composition too stifl and rigid to app satisfacpounds of silica, and any such equivalent matorily, while smaller amounts were inadequate. However, when a deliquescent alkaline earth chloride was employed we found it necessary to reduce the amount of bentonite somewhat, so

The molasses used was an ordinary table variety. The molasses-alcohol residue contained about 55% solids and 45% water by difference. The actual solid contents are the primary basis of equivalence and may be estimated from the grades as here defined. When these ingredients, separately or together, were employed with bentonite, the amounts used ranged up to about 3.5 pounds per gallon of the composition.

While a dispersion of bentonite or its equivalent may be used alone or with a hygroscopic agent comprising one or more materials, we have found it particularly desirable to employ in our treating composition botha deliquescent alkaline earth chloride and a hygroscopic sugar material. In such instances the bentonite was used in smaller amounts of about 0.2 to 0.3 pound, while the two other ingredients were used in total amounts of about 1.75 to 3.5-pounds per gallon of the treating composition, or a larger amount of bentonite was used, asfor example 0.3 to 0.5 pound, and the two other materials were used in total amounts of about 0.5 to 1.5 pounds per gallon of the composition.

A preferred form of our composition which we have found very satisfactory after extensive tests, is as follows:

Bentonite pounds 208 Calcium chloride do.. 1750 Molasses do 1250 With or without Aluminum stearate do 8 Tergitol gallons 3 Water to make 1000 gallons.

Among the many other specific forms which we have tested, the following are also set forth by way of illustration:

Bentonite pounds.. 416 Calcium chloride do 416 Water to make 1000 gallons;

Bentonite do 416 Molasses do 832 Water to make 1000 gallons;

Bentonite do 500 Glycerine or ethylene glycol do 1000 Water to make 1000 gallons.

In those of our tests, in which any other ingredients were employed with the bentonite-water dispersion, we have found it desirable that the bentonite be first dispersed in a large part of the total water to be used, after which the other ingredient or ingredients were added and the remainder of the water added to make up the total volume of the composition. I

The materials may be used in other grades or forms than those above noted, and it may be that their use will involve some changes in proportions. It is to be understood that the quan-- titles or ranges of quantities herein specified are ,by way of example and not by, way of limitapractice, be sprayed or otherwise suitably applied to the fuel to coat the same. The amount to be applied to fuel to render it dustless will depend on the size of the fuel, its dustiness and the concentration of the dust-proofing agent. Our compositions according to the present invention have proved very effective when applied to a low volatile, bituminous, x A" stoker coal in amounts from 3 to 4 gallons per ton. It is also possible to use our improved composition to wash .the coal and the coal may be passed through tanks containing the composition under such conditions of velocity as to separate the coal from the waste. The concentration of the composition in such a case may be varied by the use of more or less water according tothe specific gravity required to effect the separation and also so that the amount of the composition adhering to the coal will form an adequate coating to provide against dustiness in subsequent handling. We do not, however, restrict ourselves to any particular mode of application.

By the term solid carbonaceous fuel as employed in the claims we intend to include bituminous and anthracite coal, coke and briquettes. By the use of the term bentonite in the claims we intend to embrace any materials which possess substantially the characteristics of bentonite herein stated.

We claim as our invention: 1. The process of treating free-flowing, solid carbonaceous fuel for preventing or reducing its dustiness, which consists in applying tothe pieces of fuel, while maintaining their free-flowing character, a dust preventive film coating comprising an aqueous dispersion of bentonite in gel form.

2. The method of treating free-flowing solid carbonaceous fuel to prevent or reduce its dustiness, which consists in coating the pieces of fuel, while maintaining their free-flowing character, with an aqueous dispersion of bentonite in gel form, and a hygroscopic agent.

3. The method of treating free-flowing, solid carbonaceous fuel to prevent or reduce its dustiness, which consists in coating the pieces of fuel,

' carbonaceous fuel to prevent or reduce its dustiness,- which consists in coating the pieces of fuel, while maintaining their free-flowing character, with an aqueous dispersion of bentonite in gel form, and a hygroscopic polyhydric alcohol.

6. The method of treating free-flowing, solid carbonaceous fuel to prevent or reduce its dustiness, which consists in coating the pieces of fuel, while maintaining their free-flowing character, with an aqueous dispersion of a bentonite in, gel form, and a hygroscopic agent comprising a deliquescent alkaline earth chloride, and a hygroscopic sugar material.

'7. The method of treating free-flowing, solid carbonaceous fuel to prevent or reduce its dustiness,'which consists in coating the pieces of fuel,

while maintaining their free-flowing character;

with an aqueous dispersion of bentonite in gel form, and ahygroscopic agent comprising a deliquescent alkaline earth chloride, a hygroscopic sugar material, a heavy metal soap, and a wetting agent for such soap.

8. The method of treating free-flowing, solid carbonaceous fuel to prevent or reduce its dustiness, which consists in coating the pieces of fuel,

while maintaining their free-flowing character,

of a deliquescent alkaline earth-chloride.

11. A liquid composition for coating free-flowing, solid carbonaceous fuel to prevent or reduce its dustiness while maintaining its free-flowing character, comprising an aqueous dispersion of bentonite in gel form, and an aqueous solution of a hygroscopic sugar material.

12. A liquid composition for coating free-flowing, solid carbonaceous fuel to prevent or reduce its dustiness while maintaining its free-flowing character, comprising an aqueous dispersion of bentonite in gel form, and an aqueous solution of a hygroscopic polyhydric alcohol.

13. A liquid composition for coating free-flowing, solid carbonaceous fuel to prevent or reduce its dustiness while maintaining its free-flowing character, comprising an aqueous dispersion of bentonite in gel form, and an aqueous solution of a deliquescent alkaline earth chloride, a heavy metal soap and a wetting agent for such soap.

14. A liquid composition for coating free-flowing, solid carbonaceous fuel to prevent or reduce its dustiness while maintaining its free-flowing character, comprising an aqueous dispersion of bentonite in gel form, and an aqueous solution Bentonite pounds 208 Calcium chloride do; 1750 Molasses do 1250 Aluminum stearate do 8 wetting agent for aluminum stearate (as tergitol) gallons 3 Water in sufilcient quantity to make 1000 gallons.

17. A dust-prooi'ed solid carbonaceous fuel the pieces of which are film coated with bentonite from aqueous dispersion in gel form, and are free-flowing.

18. A dust-proofed solid carbonaceous fuel the pieces of which are film coated with bentonite from aqueous dispersion in gel form, and a hygroscopic agent, and are free-flowing.

19. A dust-proofed solid carbonaceous fuel the pieces of which are film coated with a composition containing aqueously dispersed bentonite, a deliquescent alkaline earth chloride, a heavy metal soap and a wetting agent for such soap, and are free-flowing.

20. The method of treating mined coal containing waste, which consists in washing the same in an aqueous dispersion of bentonite in gel form, to separate the coal from the waste and in and by the washing operation mount the coal with the bentonite dispersion to reduce its dustiness.

LINCOLN T. WORK. RUDOLPH E. ZE'ITERSTRAND. 

